1. Field of the Invention
The present invention relates to a silver halide photographic material and, more particularly, it relates to a silver halide photographic material having increased photosensitivity without being accompanied with the formation of fog.
2. Description of the Prior Art
In the production of silver halide photographic materials it has hitherto been desired to increase the photosensitivity and various methods have been proposed for this purpose. In particular, various investigations have been made on increasing the photosensitivity of silver halide photographic materials by incorporating therein various compounds at the chemical ripening step during the production of the photographic materials and further some of these methods have been employed industrially. As the sensitizers incorporated at the chemical ripening step described above, there are known such sulfur compounds as sodium thiosulfate, thiourea derivatives, etc.; such noble metal compounds as chloroauric acid, gold-thiosulfate complex salt, gold-rhodan complex salt, etc., and such reductive compounds are ferrous chloride and aminoiminomethanesulfonic acid. It is also known to use gelatin naturally containing sensitizers, to use a sulfur compound and a selenium compound together, to use a goldmercapto compound, and to use a gold compound and a phenol derivative together.
The practical conditions for conducting the chemical ripening treatment with or without the addition of such chemical sensitizers are restricted by the formation and increase of fog with the increase of sensitivity as the ripening progresses, that is to say, the extent of chemical ripening, i.e., the amount of the chemical sensitizer, the temperature of the chemical ripening, and the period of time for the chemical ripening are so selected that the formation of fog which is harmful is not oberserved. Also, the formation of fog during the preservation of photographic materials after coating and drying is promoted by inadequate chemical ripening and thus the conditions for chemical ripening are also restricted from this standpoint.
From the above reasons it will be easily understood that if the formation of fog is not accompanied by the progress of chemical ripening, it becomes possible to promote the extent of chemical ripening and increase the photographic sensitivity. Many compounds have been reported as antifoggants and it is known these compounds show antigogging activity. For instance, the use of benzenesulfinic acid and thiosulfonic acid together as described in U.S. Pat. No. 2,394,198, the use of benzenesulfinic acid amide as described in U.S. Pat. No. 3,498,792, the use of sugar mercaptal as described in U.S. Pat. No. 3,635,717, and the use of 1,2-glycol as described in U.S. Pat. No. 3,650,759, have been proposed. However, these compounds are insufficient for the aforesaid purpose or in other words, the desired satisfactory results are not obtained by using such known compounds.